Wide band gap semiconductor composite detector plates for x-ray digital radiography

ABSTRACT

An imaging composition for radiation detection systems which includes an admixture of at least one non-heat treated, non-ground particulate semiconductor with a polymeric binder. The non-heat treated, non-ground particulate semiconductor is selected from mercuric iodide, lead iodide, bismuth iodide, thallium bromide and cadmium-zinc-telluride (CZT), and at least 90% of the semiconductor particulates have a grain size of less than 100 microns in their largest dimension. A radiation detector plate ( 10 ) for an imaging system includes a substrate ( 12 ) which serves as an electrode, at least one imaging composition layer ( 16 ) applied onto the substrate ( 12 ), and a second electrode ( 18 ) which is in electrical connection with the imaging composition ( 16 ) and connected ( 20, 22 ) to a high voltage bias.

FIELD OF THE INVENTION

The present invention relates to wide band gap semiconductor-bindercomposites for use in detectors in X-ray digital imaging.

BACKGROUND OF THE INVENTION

Lead iodide (Pbl₂), bismuth iodide (Bil₃), thallium bromide (TIBr) andmercuric iodide (Hgl₂), are well-known wide band gap semiconductors thatexhibit properties which make them ideal for use in room temperatureX-ray detection and imaging applications. These properties include awide band gap (2.3, 2.2, 2.3 and 2.1 eV respectively), high atomicnumbers Z, and low energy (below 5 eV) electron-hole pair formation. Thewide energy band gap reduces the dark current at room temperature; thehigh atomic numbers permit good photon absorption and reduce radiationexposure; and the low energy for electron-hole pair formation produces ahigh X-ray-to-electrical charge ratio which conveys a high conversioncoefficient.

The use of mercuric iodide as single crystal X-ray detectors is knownbut limited to relatively small area detectors due to the high cost ofproducing large single crystals. Moreover, mercuric iodide crystals areproduced from the vapor phase and large crystals require long periods oftime for growth. Finally, the sawing and polishing of these crystals canresult in the loss of a large percentage, even a major portion, of thecrystal. For applications requiring large detection areas, such asdetectors having areas in excess of 100 cm², the use of polycrystallinemercuric iodide grains with their much lower production cost is veryadvantageous.

Polycrystalline Hgl₂ and Pbl₂ have been used in X-ray detector plates.U.S. Pat. No. 5,892,227, (M. Schieber, et al.) incorporated herein byreference, describes methods for producing such plates from wide-bandgap semiconductors by either direct evaporation of Hgl₂ and Pbl₂, or inthe case of Hgl₂, by mixing the condensed iodide grains with a binder toform “composite imagers”. After deposition of the polycrystallinegrains, the semiconductor is sintered to form a single, coherent,polycrystalline, continuous film.

Up until now, the signal intensities obtained when converting x-rays toelectrical signals are poorer for wide band gap semiconductor compositeimagers than for physical vapor deposition (PVD) imagers of the samesemiconductor. In some cases, the difference in electrical signalsbetween composite and PVD imagers is almost two orders of magnitudes.Additionally, the equipment required to produce PVD imagers is large andcostly. Furthermore, the substrates used with PVD coated detectorsgenerally are required to be flat, even though for certain uses, such asnon-destructive testing, curved substrates would be more desirable.

A review of prior art polycrystalline Hgl₂ can be found in the followingpublications.

-   R. Turchefta, et al., VLSI Readout for Imaging with Polycrvstalline    Mercuric Iodide Detectors, Proceedings of the SPIE Conf., San Diego    Calif., July 1998, edited by O. H. W. Siegmunds and M. A. Gummin,    Vol. 3445, (1998) 356-363.-   R. Turchetta, et al., Imaging with Polycrystalline Mercuric Iodide    Detectors using VLSI Readout, Proceedings of the Detector Workshop    held at XIIth Int. Conf. Cryst. Growth, Jerusalem, Israel, July    1998, edited by R. B. James, L. Franks, P., Nucl. Inst. and Meth. A    Vol. 428 (1999) 88-   M. Schieber, et al, High flux X-ray response of composite mercuric    iodide detectors, Hard Radiation SPIE, Denver, 1999, Vol.    3768 (1999) 296-309.-   M. Schieber, et al., Polycrystalline mercuric iodide detectors,    Medical Imaging Proc., SPIE, Denver, 1999, Vol. 3770 (1999) 146-155.-   M. Schieber, et al. Polycrystalline mercuric iodide detectors,    Medical Imaging Proc., SPIE, Denver, 1999, Vol. 3770 (1999) 146-155.-   R. Street, et al., High Resolution. Direct detection X-Ray Imagers,    Proceedings of SPIE Vol. 3977 (2000) 418.-   M Schieber, et al., Radiological X-ray Response of Polycrystalline    Mercuric Iodide Detectors, Proceedings of the SPIE Medical Imaging    2000 San Diego, Vol. 3977 (2000) 48.-   M. Schieber et al., Mercuric Iodide Thick Films for Radiological    X-ray Detectors, Proceedings of the SPIE in Penetrating radiation,    Vol 4142 (2000) 197.-   M. Schieber et al., Thick Films of X-ray Polycrystalline Mercuric    Iodide Detectors, published in JCG (8-2000)

A review of prior art polycrystalline lead iodide detectors can be foundin the following publications and in the aforementioned patent.

-   R. Street, et al., High Resolution. Direct Detection X-Ray Imagers,    Proceedings of SPIE Vol. 3977 (2000) 418.-   R. Street, et al., X-ray Imaging using Lead Iodide as a    Semiconductor Detector, Proceedings of SPIE, Vol. 3659 (1999), p.    36.-   R. Street, et al., Large Area X-Ray Image Sensing Using a Pbl2    Photoconductor, Proceedings of SPIE Vol. 3336 (1998) 24.

The films or crystals of lead iodide described in the above referenceswere all prepared using vacuum sublimation, vacuum evaporation or otherphysical vapor deposition procedures.

SUMMARY OF THE INVENTION

The present invention is directed toward producing wide band gapsemiconductor particle-in-binder (PIB) composite detectors for X-raydigital imagers. The semiconductors discussed herein include, interalia, Pbl2, Bil3, TIBr, Cd—Zn—Te (CZT) and Hgl2. The compositions,detectors and imaging systems prepared according to the presentinvention allow for better direct X-ray radiation-to-electrical signalconversion than prior art imagers. They also allow for the fabricationof detector plates and imagers with sensitivities close to the order ofmagnitude obtained by polycrystalline detector plates and imagersproduced by PVD type processes. The materials and systems describedherein permit the fabrication of low cost, large area imagers with highsensitivity.

It should be noted that with respect to what is described herein asradiation detector plates, constructions other than planar constructionsare contemplated. Therefore these radiation detector plates have attimes been more generically described as radiation detection systems.These terms are to be construed as equivalent, both including planar andnon-planar constructions. Similarly in what has been described herein,the terms particle, particulate and grain have been used interchangeablyand should be deemed to be equivalents. In a like manner, particle size,particulate size and grain size are all deemed to be equivalents.

In one aspect of the present invention, an imaging composition forradiation detection systems is described which comprises an admixture ofone or more non-heat treated and non-ground particulate semiconductorswith a polymeric binder. Ninety percent of the semiconductor particleshave a grain size less than 100 microns in their largest dimension.Typically, the non-heat treated, and non-ground particulatesemiconductor Is selected from a group consisting of mercuric iodide,lead iodide, bismuth iodide, thallium bromide and cadmium-zinc-telluride(CZT).

In another aspect of the present invention a radiation detector plate isdescribed which includes at least one substrate which serves as a bottomelectrode. It also includes at least one composition layer prepared froman imaging composition which comprises an admixture of at least onenon-heat treated, non-ground particulate semiconductor with a polymericbinder. At least ninety percent of the semiconductor particles in thedetector plates have a grain size of less than 100 microns In theirlargest dimension. Typically, the semiconductor is chosen from a groupconsisting of bismuth iodide, lead iodide, mercuric iodide, thalliumbromide and cadmium-zinc-telluride (CZT). The detector plate furtherincludes an upper electrode which is in electrical connection with thecomposition layer and which is also connected to a high voltage bias.

In a further aspect of the present invention, an image receptor for animaging system is described. The receptor comprises at least onecomposition layer comprised as defined in the above described detectorplate. The composition layer is positioned on a conductive substratelayer, which forms a bottom electrode. The composition layer is coveredby an upper conductive layer, which forms an upper electrode. At leastone of the conductive layers is provided with a plurality of conductiveareas separated from each other by a plurality of non-conductive areas.A multiplicity of the conductive areas are individually connected, via acharge-sensitive pre-amplifier, to an imaging electronic system.

Finally, in another aspect of the present invention, a method forpreparing radiation detector plates is described.

There is thus provided in accordance with the present invention, animaging composition for radiation detection systems which comprises anadmixture of one or more non-heat treated, and non-ground particulatesemiconductor with a polymeric binder, wherein at least 90% of thesemiconductor particles have a grain size less than 100 microns in theirlargest dimension. The non-heat treated, and non-ground particulatesemiconductor is selected from a group consisting of mercuric iodide,lead iodide, bismuth iodide, thallium bromide and cadmium-zinc-telluride(CZT).

In a preferred embodiment of the invention, the imaging compositionpossesses at least one of the following features:

-   -   the polymeric binder is an organic polymeric binder;    -   at least 90% of the semiconductor particles has a grain size of        less than 15 microns in their largest dimension;    -   the composition further comprises at least one organic solvent;    -   the weight ratio of the semiconductor particulates to the binder        is from about 4.4:1 to about 26.0:1.

In another embodiment of the present invention, the imaging compositionpossesses at least one of the following features:

-   -   the organic polymeric binder comprises at least one polymer        selected from a group consisting of polystyrene, polyurethane,        alkyd polymers, cellulose polymers, and acrylic and vinyl        polymers and co-polymers and mixtures thereof;    -   at least 90% of the semiconductor particles have a grain size of        less than 10 microns in their largest dimension;    -   the at least one organic solvent is selected from aliphatic        alcohols, ethers, esters, ketones and aromatic and heterocyclic        solvents;    -   the weight ratio of the semiconductor particulates to the binder        is from about 6.6:1 to about 19.8:1.

In yet another embodiment, the imaging composition possesses at leastone of the following features:

-   -   the organic polymeric binder comprises one or more polymer        selected from polystyrene, polyurethane, and acrylic and vinyl        homo- and co-polymers and mixtures thereof;    -   at least 90% of the semiconductor particles has a grain size of        less than 5 microns in their largest dimension;    -   the at least one organic solvent is selected from aliphatic        alcohols, ethers, esters, ketones and aromatic and heterocyclic        solvents;    -   the weight ratio of the semiconductor particulates to the binder        is from about 9:1 to about 15.4:1.

In a further embodiment of the invention, the semiconductor particulatesof the imaging composition are precipitated from a solution. Thesolution has a solvent which is chosen from a group consisting of water,a non-aqueous solvent, a mixed aqueous-non-aqueous solvent and a mixednon-aqueous solvent.

Additionally there is provided in accordance with the present inventiona radiation detector plate. The plate includes at least one substrate,which serves as an electrode. The detector plate further includes atleast one imaging composition layer prepared from an imagingcomposition. The composition comprises an admixture of at least onenon-heat treated, non-ground particulate semiconductor with a polymericbinder, with at least 90% of the semiconductor particles having a grainsize of less than 100 microns in their largest dimension. Thesemiconductor is typically chosen from a group consisting of bismuthiodide, lead iodide, mercuric iodide, thallium bromide andcadmium-zinc-telluride (CZT). The composite layer is applied onto thesubstrate. The detector plate also includes a second electrode, which isin electrical connection with the composition layer and with a highvoltage bias.

In a further embodiment of the present invention, the radiation detectorplate additionally comprises at least one composition layer comprisingnon-heat treated, non-ground particulate mercuric iodide in admixturewith a polymeric binder.

In another embodiment of the radiation detector plate, the at least onecomposition layer of the radiation detector plate comprises at least twosemiconductors selected from a group consisting of bismuth iodide, leadiodide, mercuric iodide, thallium bromide and cadmium-zinc-telluride(CZT).

Additionally, in an embodiment of the radiation detector plate, the atleast one composition layer comprises at least two discrete compositionlayers, each of the discrete layers comprised of at least onesemiconductor selected from a group consisting of bismuth iodide, leadiodide, mercuric iodide, thallium bromide and cadmium-zinc-telluride(CZT).

In another embodiment, the detector plate further includes an adhesivelayer between the discrete composition layers.

In a preferred embodiment of the radiation detector plate, the at leasttwo discrete composition layers comprise at least one discretecomposition layer where the semiconductor is non-heat treated,non-ground particulate lead iodide and at least one discrete compositionlayer where the semiconductor is non-heat treated, non-groundparticulate mercuric iodide.

In another embodiment, the detector plate further includes an adhesivetie layer applied to the substrate, the adhesive chosen from a groupconsisting of polyacrylics, polyvinyls, polyurethanes, polyimides,cyanoacrylics, silanes, polyesters, and neoprene rubbers and mixturesthereof.

In one embodiment the of the detector plate, the tie layer is apolyacrylic-polyvinyl mixture, while in another embodiment the tie layeris a silane.

In a further embodiment of the detector plate, the substrate is coatedwith a uniform thin film of electrically conducting material selectedfrom palladium, gold, platinum, indium-tin oxide and germanium.

In yet another embodiment of the detector plate, the second electrodeincludes a uniform thin film of electrically conducting materialselected from carbon, palladium, gold, platinum, indium-tin oxide andgermanium. The second electrode can be applied by spraying, painting,sputtering and evaporation.

In yet another embodiment of the detector plate, the one or moresubstrates is chosen from a group consisting of thin film transistor(TFT) flat panel array, a charge coupled device (CCD), complementarymetal oxide semiconductor (CMOS) array and an application specificintegrated circuit (ASIC).

In a preferred embodiment of the radiation detector plate according tothe present invention, the at least one composition layer possesses atleast one of the following features:

-   -   the polymeric binder is an organic binder;    -   at least 90% of the semiconductor particles have a grain size of        less than 15 microns in their largest dimension.

In yet another embodiment of the radiation detector plate, the at leastone composition layer possesses at least one of the following features:

-   -   the organic polymeric binder comprises one or more polymers        selected from polystyrene, polyurethane, alkyd polymers,        cellulose polymers, and acrylic and vinyl homo- and co-polymers        and mixtures thereof;    -   at least 90% of the semiconductor particles have a grain size of        less than 10 microns in their largest dimension.

In another embodiment of the radiation detector plate, the at least onecomposition layer possesses at least one of the following features:

-   -   the organic polymeric binder comprises at least one polymer        selected from polystyrene, polyurethane, and acrylic and vinyl        homo- and co-polymers and mixtures thereof;    -   at least 90% of the semiconductor particles have a grain size of        less than 5 microns in their largest dimension.

Additionally, in an embodiment of the invention, the one or morecomposition layers of the detector plate is prepared at roomtemperature. In a further embodiment, the one or more composition layersof the detector plate is prepared at temperatures below 60° C.

In an embodiment of the invention, the at least one composition layer ofthe detector plate has a thickness of 40-3000 microns. In anotherembodiment of the detector plate, the plate can detect radiation in the6 keV to 15 MeV range.

In another aspect of the present invention, there is also provided animage receptor for an imaging system. The receptor comprises at leastone composition layer comprised of an imaging composition as describedabove. The composition layer is positioned on a conductive substratelayer, the substrate layer forming a bottom electrode. The compositionlayer is covered by an upper conductive layer, which forms an upperelectrode. At least one of the conductive layers is provided with aplurality of conductive areas separated from each other by a pluralityof non-conductive areas. A multiplicity of the conductive areas areindividually connected, via a charge-sensitive pre-amplifier, to animaging electronic system.

In a preferred embodiment of the image receptor, the receptor is furthercharacterized by at least one of the following features:

-   -   the conductive areas are separated from each other by a        dielectric material;    -   the conductive substrate layer is covered with a uniform, thin        film electrode layer selected from the group consisting of        palladium, gold, platinum, indium-tin oxide (ITO) and germanium;    -   the image receptor is adapted for use in an imaging system        selected from X-ray and gamma ray imaging systems;    -   in the at least one composition layer, the polymeric binder is        an organic binder;    -   in the at least one composition layer, at least 90% of the        semiconductor particles have a grain size of less than 15        microns in their largest dimension;    -   an adhesive tie layer between the composition layer and the        bottom electrode, the tie layer chosen from a group consisting        of polyacrylics, polyvinyls, polyurethanes, polyimides,        cyanoacrylics, silanes, polyesters, and neoprene rubbers and        mixtures thereof to bind the composition layer to the electrode.

In another embodiment of the image receptor, the at least onecomposition layer possesses at least one of the following features:

-   -   the organic polymeric binder comprises at least one polymer        selected from polystyrene, polyurethane, alkyd polymers,        cellulose polymers, and acrylic and vinyl homo- and co-polymers        or mixtures thereof;    -   at least 90% of the semiconductor particles have a grain size of        less than 10 microns in their largest dimension.

In another embodiment of the image receptor, the at least onecomposition layer possesses at least one of the following features:

-   -   the organic polymeric binder comprises at least one polymer        selected from polystyrene, polyurethane, alkyd polymers,        cellulose polymers, and acrylic and vinyl homo- and co-polymers        or mixtures thereof;    -   at least 90% of the semiconductor particles have a grain size of        less than 5 microns in their largest dimension.

In a further embodiment of the image receptor, the receptor comprisesadditionally at least one composition layer comprising non-heat treated,non-ground particulate mercuric iodide in admixture with an organicpolymeric binder.

In yet another embodiment of the image receptor, the at least onecomposition layer comprises at least two semiconductors selected from agroup consisting of bismuth iodide, lead iodide, mercuric iodide,thallium bromide and cadmium-zinc-telluride (CZT).

In a further embodiment of the image receptor, the at least onecomposition layer comprises at least two discrete composition layers,each of the discrete layers comprised of at least one semiconductorselected from a group consisting of bismuth iodide, lead iodide,mercuric iodide, thallium bromide and cadmium-zinc-telluride (CZT).

Additionally, in another preferred embodiment of the image receptor theat least two discrete composition layers comprise at least one discretecomposition layer where the semiconductor is non-heat treated,non-ground particulate lead iodide and at least one discrete compositionlayer where the semiconductor is non-heat treated, non-groundparticulate mercuric iodide.

In yet another embodiment of the present invention, the image receptorfurther comprises an adhesive layer between the two discrete compositionlayers.

In yet another embodiment of the image receptor, the substrate is chosenfrom a group consisting of a thin film transistor (TFT) flat panelarray, a charge coupled device (CCD), a complementary metal oxidesemiconductor (CMOS) array and an application specific integratedcircuit (ASIC).

In another embodiment of the receptor, the receptor is prepared at roomtemperature. In yet another embodiment of the receptor, the receptor isprepared at temperatures below 60° C.

In another embodiment of the image receptor, the receptor can detectradiation in the 6 keV to 15 MeV range.

Additionally, there is provided in accordance with the present inventiona method for preparing a radiation detector plate, the method Includingthe steps of:

-   -   providing a substrate;    -   placing a semiconductor imaging composition onto the substrate,        thereby forming a composition layer;    -   applying an electrode to the composition layer on the side        distal from the substrate; and    -   connecting a high voltage bias connection to the electrode.

In an embodiment of the invention, the above method for preparing aradiation detector plate further comprises the step of applying anadhesive tie layer to the substrate prior to the placing step.

In an another embodiment of the method for preparing a radiationdetector plate, the placing step further comprises a step of diepressing the composition to form the composition layer. In otherembodiments of the method, the placing step further comprises a step ofslot die coating the composition to form the composition layer; theplacing step further comprises a step of spreading the composition witha doctor blade to form the composition layer; the placing step furthercomprises a step of spreading the composition with a Mayer rod to formthe composition layer; the placing step further includes the step ofscreen printing the composition to form the composition layer.

In yet another embodiment of the method, the placing step includes aseries of placing steps each of the steps forming another compositionlayer.

Finally in another embodiment of the method, the method furthercomprises the step of depositing an electrically conductive material onthe substrate before the placing step.

These and other objects, features, advantages and embodiments of thepresent invention will become apparent in light of the detaileddescription of the embodiments thereof, as illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description taken in conjunction with thedrawings in which:

FIG. 1 is a schematic representation of the layers in a wide band gapsemiconductor PIB composite detector prepared according to an embodimentof the present invention;

FIG. 2 is a schematic illustration of a pixel equivalent circuit forphotoconductor imagers according to prior art;

FIG. 3 is a schematic illustration of the die press used to form thesemiconductor PIB composite detector prepared according to an embodimentof the present invention;

FIG. 4 is a schematic illustration of the doctor blade assembly used toform the semiconductor PIB composite detector prepared according to anembodiment of the present invention;

FIG. 5 is a schematic illustration of top and side views, respectively,the screen printing apparatus used to form the semiconductor PIBcomposite detector prepared according to an embodiment of the presentinvention;

FIG. 6 is a graph comparing the sensitivities of a prior art PVDproduced Hgl₂ detector and a composite detector prepared according to anembodiment of the present invention;

FIG. 7 is a graph comparing the sensitivities of a prior art compositedetector plate and a composite detector plate prepared according to anembodiment of the present invention;

FIG. 8 is a graph showing sensitivity of mercuric iodide-bindercomposite detectors having different grain sizes prepared according toembodiments of the present invention;

FIG. 9 is a graph showing the sensitivity at different radiation dosesof detectors having different grain sizes prepared according toembodiments of the present invention;

FIG. 10 is a graph showing the sensitivity of detector plates made fromground and non-ground mercuric iodide particles prepared according toembodiments of the present invention;

FIG. 11 is a graph showing the effect on signal-to-noise ratio of heattreatment on Hgl₂-binder composite detectors prepared according toembodiments of the present invention;

FIG. 12 is a graph comparing the sensitivity of a PVD produced Hgl₂detector and various PIB composite detectors prepared according to anembodiment of the present invention;

FIG. 13 is a graph comparing the sensitivities of PVD mercuric iodide,PVD lead iodide, screen printed mercuric iodide and screen printed leadiodide detectors;

FIG. 14 is a schematic diagram of a hybrid bi-layer detector constructedaccording to a preferred embodiment of the present invention; and

FIG. 15 is a graph showing the bi-polarity of a Hgl₂/Pbl₂/substratehybrid composite detector constructed according to the presentinvention.

In the drawings, similar parts have been given similar numbersthroughout.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is directed towards producing wide band gapsemiconductor-binder composite detectors—herein also calledparticle-in-binder (PIB) detectors—for use in X-ray digital imagers. Thecomposites, detectors and imaging systems and methods of preparationthereof, as described herein, allow for much better directX-ray—electrical charge conversion than those of the prior art, therebyproducing the first usable digital composite imagers employing thematerials discussed herein. The materials and systems described hereinpermit low cost fabrication of large area composite imagers. Thecomposite can be applied to substrates by any of several methods knownin the art, including screen printing (SP), die pressing, doctor blade,slot coater and Mayer rod.

The direct synthesis of the semiconductor particles by precipitation,according to one aspect of the present invention, as describedhereinafter produces smaller grain sizes than does the vapor depositionprocess of prior art methods. Furthermore, the method does not requiregrinding of the resultant crystals to reduce grain size, therebypreventing morphological deterioration or undesirable phasetransformations. The absence of any heat treatment, annealing and/orsintering, allows for easy, low-cost, rapid processing.

Wide band gap semiconductors discussed herein include inter alia Hgl₂,Pbl₂, Bil₃, TIBr and CZT (cadmium-zinc-telluride). Surprisingly, thesesemiconductors, when prepared and introduced as PIB composites indetectors for use in X-ray imagers in accordance with the presentinvention, provide much improved signal sensitivity. This isparticularly true of Pbl₂. The difference in sensitivity between Pb andHg PVD detectors is about one order of magnitude, while the differencein sensitivity between mercury and lead PIB composite detectors is lessthan an order of magnitude. Also surprisingly, these semiconductor PIBcomposites when applied as base layers in Hgl₂ PIB composite detectorscan extend detector lifetimes.

It should be noted that with respect to what is described herein asradiation detector plates, other than planar constructions arecontemplated. Therefore these radiation detection plates have at timesbeen more generically described as radiation detection systems. Theseterms are to be construed as equivalent, both including planar andnon-planar constructions.

Reference is now made to FIG. 1 where a photo-conducting detector plate10 for an X-ray imaging system is shown, wherein the detector plate 10is made from a wide band gap semiconductor PIB composite producedaccording to the present invention. Detector plate 10 consists of a thinfilm transistor (TFT) substrate 12 having metallic pixels (not shown),the latter functioning as the bottom electrodes of detector 10. Oftenthese bottom electrodes are formed from indium-tin oxide (ITO). Thebottom pixel electrodes are often coated with a tie layer 14, such asHumiseal® 1B12 (a polyacrylic, polyvinyl mixture dissolved in a mixedmethyl ethyl ketone/toluene solvent), a polyimide or a silane. Tie layer14 acts as an adhesive that prevents a semiconductor PIB composite 16from peeling off the bottom pixel electrodes. Tie layer 14 is usuallyless than 0.5 micron thick, and is generally applied by dipping thesubstrate into a dilute solution of the adhesive, from which the solventis subsequently allowed to evaporate. Alternatively, tie layer 14 can bepainted onto the upper surface of the bottom pixel electrodes or spincoated onto the substrate.

A layer consisting of semiconductor PIB composite 16 can be applieddirectly onto adhesive coated substrate 12 by any of the methodsdescribed herein below. These methods include, but are not limited to,use of a doctor blade, Mayer rod, slot coater, die press or screenprinting (SP). A vacuum deposited, painted or sprayed continuous upperelectrode 18 covers the semiconductor PIB composite layer 16 on the sidedistal from substrate 12. A high voltage platinum bias wire 22 isattached to upper electrode 18 using a conductive glue 20. The lattercan be chosen from any of several commercially available glues.Optionally, the complete detector plate 10 can be mechanicallyencapsulated with Parylene, Humiseal® 1B12, or some other suchinsulating, inert material (not shown in FIG. 1), and connected to apixel array imager readout electronics unit. The readout electronicsunit is connected to a PC and the images acquired can be evaluated withimage viewing and acquisition software.

Semiconductor PIB composite layer 16 acts as a photoconductingsemiconductor in room temperature X-ray radiation detector 10 of FIG. 1.Substrate 12 of FIG. 1 is generally either a pixel readout flat panel(FP), charge coupled device (CCD), complementary metal oxidesemiconductor (CMOS) array or application specific integrated circuit(ASIC). These substrates are commercially available, and may beconnected to readout units such as the one mentioned above.

Typical FP and CCD substrates used for detector 10 of FIG. 1 containsquare pixels having a conductive coating, the latter serving as thebottom pixel electrodes for the detector. The pixels are typically about100×100 microns, and each pixel is separated from its nearest neighborsin all directions by about 10-15 microns.

Reference is now made to FIG. 2 which illustrates a typical prior artpixel equivalent circuit 40 for a photoconducter detector 44 plate in anX-ray imaging system. Circuit 40 shows one detector electrode 58connected to a bias voltage 50. The second electrode 56 is connected toa storage capacitor 46 and an a-Si:H (amorphous silicon) switchingthin-film transistor (TFT) 42. Storage capacitor 46 is connected to aground plane 48. Thin-film transistor 42 is connected to both a gateline 54 and a data line 52, with data being fed to a readout unit (notshown) through data line 52. Except for the contact between the secondelectrode 56 of detector 44 to TFT 42, the rest of the pixel is isolatedfrom the detector's 44 electrodes 58 and 56 by an insulation layer.

Reference is now made to FIGS. 3-5 where three coating methods are shownwhich can be used to apply the wide band gap semiconductor PIBcomposites of the present invention to substrates. These three coatingmethods are exemplary only and should not be considered limiting withrespect to other coating methods which also could be used.

FIG. 3 shows a die press 60 that may be used to prepare detectors fromthe composite photoconductor material taught in the present invention.The pressing operation is effected at room temperature at relatively lowpressures 40-100 g/cm², preferably about 50 g/cm². Die press 60 can bevibrated before or during pressing to reduce undesirable voids in thecomposite layer 64 of the detector.

FIG. 3 shows a mold 68 containing an adhesive-coated substrate 66 onwhich a wide band gap semiconductor PIB composite 64 is placed.Composite 64 is quickly pressed at room temperature with punch 62, afterwhich punch 62 and die holder 62A are displaced laterally along the topof mold 68 leaving a substantially level composite surface. The detectorlayers 64 and 66 can be left to dry at room temperature in mold 68 ormore preferably dried after removal from mold 68.

FIG. 4, to which reference is now made, shows a doctor blade assembly 70used to form the composite layer in the detector of the presentinvention. Mold 78 contains an adhesive coated substrate-76 upon which awide band gap semiconductor PIB composite 74 prepared according to thepresent invention is deposited. A doctor blade 72 then moves laterallyacross the face of mold 78, removing excess material, resulting in asubstantially level top surface of the composite. The detector 74 and 76is then removed from mold 78 and allowed to dry at room temperature.When using the die press of FIG. 3 or doctor blade assembly of FIG. 4,the final thickness of the detector is controlled by using spacershaving appropriate thickness.

Reference is now made to FIG. 5, which shows top and side views of ascreen print assembly 80 which can be used to produce detectors from thecomposite material taught in the present disclosure. The composite isapplied in layers, each layer usually being about 40 microns thick. Thethickness of each layer is generally determined by the thickness of themesh 84. The total thickness of the composite layer in the detector canreach 3 mm or more which is adequate for use with X-rays having energiesin the range up to several tens of MeV. Currently, the size of theplates can be 17″×17″, which is the current state of the art forpixilated substrates; however, there is no intrinsic limitation toproducing significantly larger plates. There is also no intrinsiclimitation to fabricating plates having thicknesses which can be usedwith radiation on the order of GEVs.

FIG. 5 shows uncoated 84 and resin coated 86 meshes both housed in analuminum frame 88. A leveling element, here a squeegee 82, moves acrossthe surface of meshes 84 and 86. An adhesive coated substrate 94, oftena Humiseal® 1B12 coated substrate is placed below mesh 84 and 86 and themercuric-iodide binder composite is spread over the screen and squeegeedthrough the mesh. The squeegeed composite forms a relatively level layer96. The substrate 94 can be repeatedly lowered so that successive layersof the composite can be added. Typically, the layers are on the order of40 microns with the number of layers applied determining the totalthickness of detector 94 and 96.

The adhesive tie layer described herein above in conjunction with FIGS.1, 3, 4 and 5 is in fact an optional layer, needed only when the binderin the composite can not adhere directly to the bottom electrode. Incases where the binder adheres directly to the electrode, an adhesivetie layer is not needed. The tie layer therefore is not obligatory inall embodiments and should be construed as such throughout thediscussion herein.

The detector plates produced by any of the three methods described aboveis dried, generally at room temperature. It can be dried at somewhathigher temperatures, but never at temperatures in excess of 60° C.

After drying, a continuous upper electrode such as gold or a carbonbased contact is deposited. The upper electrode can be deposited usingany of a number of methods including vacuum deposition, sputtering,painting or spraying. Gold electrodes are preferably applied viasputtering. Carbon electrodes are generally applied by painting orspraying a carbonaceous dispersion that forms a substantially continuouselectrode layer when dry. If desired, a metal layer can be furtherdeposited on the carbon layer to increase electrical conductivity. Otherelectrode materials that do not react with wide band gap semiconductormaterials, such as those enumerated below, also can be used to form acontinuous upper electrode. They can be applied by the methods describedherein above.

A high voltage platinum wire is then attached to the continuous upperelectrode by means of any of a number of commercially availableconducting glues. Particularly preferable are conducting carbon basedadhesives. The platinum, wire serves as a high voltage bias connectorthat can be connected to the readout electronics. Images are obtainedfrom the readout electronics and displayed. Details of the readoutelectronics receiving the digital data generated by the detector hasbeen described elsewhere, for example in the publication of Street etal., Proc. SPIE Vol 3977 (2000), 418, cited above.

The present invention inter alia provides for a Hgl₂—binder compositedetector plate which can attain about 40-50% of the sensitivity obtainedby non-composite polycrystalline Hgl₂—PVD produced imagers. Referring toFIG. 6, the heightened sensitivity of Hgl₂—binder composite detectorsprepared according to the present invention is readily seen. Theimproved direct conversion of X-rays to electrical charges in compositeimagers which use materials of the present invention produces goodquality digital images. Furthermore, the ease of fabrication, their lowcost, and the increase in safety of these composite imagers make themmore desirable than PVD fabricated imagers.

It has been found that the direct precipitation of the startingmaterial, mercuric iodide, from aqueous solution is important inpreparing high-quality mercuric iodide-binder composite detectors. Thismethod ensures small grain size, something that prior art preparationmethods, such as repeated evaporation and sublimation, are unable to do.The size of repeatedly sublimed mercuric iodide grains is usually 50-300microns; grinding is required to obtain smaller grain sizes. Grindinghowever harms the morphology of the resulting grains because it inducesplastic deformations. These deformations may act as electron traps,interfering with the sensitivity of the composite detector plates madewith such ground grains.

Acceptable results are obtained by precipitating Hgl₂ directly from anaqueous solution, starting with stoichiometrically matched molarsolutions of mercuric chloride and potassium iodide e.g. a solution of0.6 M HgCl₂ and a solution of 1.2 M KI. The starting iodide and chlorideshould be at least 99%, or more preferably 99.9%, pure, purities readilyavailable commercially. The two reagents are added slowly and thesolution mixed vigorously with a mechanical or magnetic stirrer. Theprecipitated Hgl₂ is washed with water, filtered, and dried. Thewashing, filtering and drying cycles can be repeated a number of timesbut no additional purification procedures are needed. The material isthen sieved and separated into fractions based on grain size. Thepreferred fraction for preparing composite detectors is mercuric iodidehaving grain diameters of 100 microns or less, more preferably 15microns or less, 10 microns or less, or 5 micron or less.

While the above has discussed precipitation from aqueous solution, thisshould be considered as exemplary only and not limiting. Similarly,while HgCl₂ and KI are discussed herein, it is readily appreciated thatother soluble mercuric and iodide salts can also be used in thesynthesis of mercuric iodide. Precipitation of Hgl₂ can be effected frommany non-aqueous solvents, or mixed non-aqueous solvent systems or mixedaqueous-non-aqueous solvent systems as well, when mercuric and iodidesalts soluble in such solvents are used. Non-aqueous solvents which canbe used include for example acetone, methanol, ethanol, dimethylsulfoxide, and toluene.

The powder obtained is then mixed with a binder, generally an organicbinder but other binders such as silicon based binders can be used aswell. Binders which can be used include binders chosen from thefollowing classes: acrylic and methacrylic ester polymers, polymerizedester derivatives of acrylic and alpha-acrylic acids, polymerized butylmethacrylates, chlorinated rubber, vinyl polymers and co-polymers suchas polyvinyl chloride and polyvinyl acetate, cellulose esters andethers, alkyd resins and silicones. Mixtures of such resins or mixturesof such resins and conventional plasticizers, such as phthalates,adipates and phosphates, may also be used. Particularly preferable asbinders are polystyrene and Humiseal® 1B12, the latter apolyacrylic-polyvinyl blend. In situ polymerization of the binder, forexample, styrene, using peroxide catalysts can also be employed.

When polystyrene is used as the binder a colloidal solution of, forexample, 25 wt % of the polymer in toluene is prepared. In order toobtain faster dissolution of the polystyrene in toluene, the mixture canbe heated gently and then slowly cooled to room temperature. Themercuric iodide powder prepared as described above is then mixed in theweight ratio of Hgl₂ to dried polystyrene of between 4.4:1 and 26.0:1,preferably between 6.6:1 and 19.8:1 and even more preferably 9.0:1 and15.4:1. Similar ratios can be used with other binders. The material ismixed thoroughly to wet all of the mercuric iodide powder and to obtaina homogenous mixture.

The TFT flat panel arrays or CCD substrate is coated with a less than0.5 micron tie layer of an adhesive such as Humiseal® 1B12, otherpolyacrylics, polyvinyls, polyurethanes, polyimides, silanes,cyanoacrylics, polyesters, neoprene rubbers or mixtures thereof. Theadhesive is generally applied by dipping the substrate into a dilutesolution of the adhesive and evaporating off the solvent. Spin coatingof the adhesive onto the substrate can also be used. Alternatively, theadhesive can be painted or sprayed on above the bottom pixel electrodes.After the adhesive is applied, the Hgl₂— binder composite is placed ontothe adhesive layer by any of the methods described herein above.

In order to achieve long lifetimes for the imager, both the bottom andtop electrodes can be made of indium-tin oxide (ITO), gold, carbon,silicon, germanium, chromium, nickel, platinum or palladium electrodes.These latter materials do not react significantly with mercuric iodide.When a carbon electrode is used a metal layer can be deposited on it tofurther increase conductivity. It is inadvisable to usetitanium-tungsten alloy (Ti—W), In, Al, or Cu because they react withthe mercuric iodide composite.

Reference is now made to FIG. 7 where a graph of sensitivity versus biasis shown for detectors made with mercuric iodide composites prepared asdescribed in prior art (U.S. Pat. No. 5,892,227) and the presentinvention. Detector plates using mercuric iodide-binder compositesprepared according to the present invention show sensitivities about 1.5orders of magnitude greater than plates prepared using compositesprepared according to prior art. This may be a result of the small sizeof the grains used, their non-deformed morphology, or the lack of anyheat treatment, or a combination of these factors.

Reference is now made to FIGS. 8-11, which show the effect of grainsize, radiation dosage, grinding and heat treatment on sensitivity andsignal-to-noise ratio for mercuric iodide composite detectors.

FIG. 8 shows the effect of grain size on sensitivity. Surprisingly,smaller grain size leads to better sensitivity at low operating bias. Inview of the fact that single crystal mercuric iodide detectors exhibithigher sensitivities than polycrystalline detectors, it would have beenexpected that detectors with larger Hgl₂ grains would show highersensitivities than detectors using smaller Hgl₂ grains. FIG. 8 showsthat the opposite is true.

As can also be seen, the performance of the detector made from smallergrains compared to the detector made from larger grains remainssubstantially unchanged above a certain operating bias, here about 300V. This indicates that higher biases are not advantageous especiallysince dark current increases very much more rapidly at higher biases.Importantly, FIG. 9 shows that while smaller particles provide bettersensitivity than larger grains, the effect is more pronounced at thelower radiation doses (8 mR) commonly used in medical imaging.

As mentioned above, material synthesized by aqueous precipitation canproduce relatively small grains that do not require grinding. Sievingalone is sufficient to produce fractions of particles 90% of which havediameters of 5 microns or less as determined by SEM photographs andmicroscopic inspection. Prior art detectors using mercuric iodideproduced after multiple sublimations do not produce particles of smallsize without further processing i.e. grinding. Typically, multiplesublimation produces particles in the 50-300 micron range. As shown inFIG. 10, particles that are not ground display higher sensitivities thanparticles that are ground. It is posited that this is a result ofplastic deformations introduced by grinding.

Finally, FIG. 11 shows the effect of heat treatment on the signal tonoise (S/N) ratio of composite detectors. The heat-treated detector washeated at 120° C. for 10 minutes under a pressure of 1 kg/cm². FIG. 11shows that heat treatment degrades the performance of mercuriciodide-binder composites. It should be noted that the use of the term“heat treatment” or “heat treated” herein encompasses inter aliasintering and/or annealing. Thus the Hgl₂ used in the present inventionis neither sintered nor annealed, since such operations require heattreatment.

EXAMPLE 1

A 0.6 M aqueous solution of HgCl2 and a 1.2 M aqueous solution of KIwere mixed quickly in a container. The Hgl₂ which precipitated waswashed with water, filtered and dried, the washing, filtering and dryingcycle being repeated three times. The mixture was then sieved andseparated into fractions by grain size. The fraction passing through the20 micron sieve was used and microscopic inspection of that fractionshowed that more than 90% of the particles had a diameter of 5 micronsor less. The mercuric iodide particulates were then mixed with a 25 wt %polystyrene/toluene solution. The homogeneous mixture obtained had aweight ratio of Hgl₂ to dry polystyrene of about 4.4:1.

A TFT substrate was coated with indium-tin oxide (ITO) to which a thinadhesive tie layer (Humiseal® 1B12) was applied. The ITO layer served asthe bottom pixel electrode. The pixels had a size of about 100×100microns, each separated by about 10 microns. The adhesive tie layer hada thickness of less than 0.5 micron and was applied by dipping thebottom pixel electrodes of the substrate into a dilute solution of theadhesive after which the solvent was allowed to evaporate.

The TFT substrate was then placed in a die press similar to the oneshown in FIG. 3 and the mercuric iodide-polystyrene composite mixturewas deposited on top of the Humiseal® tie layer. The detector plate hada final thickness of 150 microns and it had an active area of 2″×2″. Thethickness was controlled by placing a spacer having the desiredthickness in the die.

The detector plate was then removed from the die and allowed to dry atroom temperature. After drying, a continuous upper electrode of gold wasapplied by vacuum evaporation. A thin Pt wire was attached to the uppercontinuous electrode using a conductive glue; the Pt wire served as ahigh voltage bias contact.

EXAMPLE 2

As in Example 1, but instead of placing the Hgl₂/polystyrene mixture ina die press, the mixture was placed in a doctor blade assembly similarto the one shown in FIG. 4.

EXAMPLE 3

As in Example 1, but instead of placing the Hgl₂/polystyrene mixture ina die press, the mixture was placed on a screen printing apparatussimilar to the one shown in FIG. 5.

EXAMPLE 4

As in Example 1, but instead of casting the Hgl₂/polystyrene mixture ona TFT substrate array, placed in a die press, the mixture was cast on aCCD pixel array with pixel dimensions similar to that disclosed inExample 1.

EXAMPLE 5

As in Example 1, but instead of using polystyrene as the binder in thecomposite, Humiseal, a polyacrylic-polyvinyl polymeric mixture dilutedwith toluene and methyl ethyl ketone, was used as the binder. TheHumiseal®/Hgl₂ ratio was the same as in Example 1 and the detector wascast in a die press.

EXAMPLE 6

Instead of using vacuum evaporated gold as the continuous upperelectrode as in Example 1, magnetron sputtered gold was used as thecontinuous upper electrode. All other preparation steps were identicalto those described in Example 1.

While the present invention has been described herein above in terms ofmercuric iodide synthesized by precipitation from solution, the methodof preparation discussed and the examples described should be viewed asillustrative only and non-limiting. It is readily appreciated by oneskilled in the art that any method of preparing mercuric iodide whichresults in small grains of the size defined herein which do not requiregrinding and heat treatment can also be used. For example, the reactionof elemental mercury and iodine can be used to produce Hgl₂ having smallgrain sizes.

The adhesive tie layer described hereinabove in conjunction with FIGS.1, 3, 4 and 5 is in fact an optional layer, needed only when the binderin the composite does not adhere directly to the bottom electrode. Incases where the particle-in-binder (PIB) composite adheres directly tothe electrode, an adhesive tie layer is not needed. The tie layer,therefore, is not an essential element in every embodiment and shouldnot be construed as such throughout the discussion herein.

In a modification of the compositions, detectors and imaging systems ofthe present invention, it has been found possible to replace mercuriciodide by one or more particulate iodides or bromides selected frombismuth iodide, lead iodide and bismuth iodide, lead iodide, mercuricand thallium bromide. Small grain size cadmium-zinc-telluride (CZT) canalso be used. The preparation of these wide band gap semiconductorparticles, compositions, and detectors uses methods, procedures andmaterials substantially identical to those described above, inconjunction with mercuric iodide particles, compositions, detectors andimaging sytems.

The present invention provides wide band gap semiconductor PIB compositedetectors that can attain sensitivities on the order of magnitude oftheir corresponding polycrystalline PVD produced detectors. For example,as mentioned previously, a Hgl₂ PIB composite detector plate prepared bythe present invention can attain about 40-50% of the sensitivityobtained by non-composite polycrystalline Hgl₂—PVD produced imagers. Inaddition, the PIB composite detectors discussed herein, particularly PIBPbl₂ composite detectors surprisingly can attain results on the order ofmagnitude of Hgl₂ PIB composite detectors. This result is surprising inview of the fact that the difference in sensitivity of the two materialsin prior art detectors is often two or more orders of magnitude.

Referring to FIG. 12, the heightened sensitivity of composite detectorsprepared according to the present invention is readily seen. The Pbl₂PIB composite detector shows sensitivities of the same order ofmagnitude of its sister PVD Pbl₂ detector. At the same time the Pbl₂ PIBcomposite detector is only less than an order of magnitude lower thanthat of the mercuric iodide PIB detector. The improved direct conversionof X-rays-to-electrical charges in composite imagers which use materialsof the present invention produce usable quality digital images.Furthermore, the ease of fabrication, their low cost, and the increasein safety of these composite imagers make them more desirable than PVDfabricated imagers.

Reference is now made to FIG. 13 where a graph of sensitivity versusbias is shown for mercuric iodide and lead iodide detectors prepared byboth the PVD method and the PIB composite method according to thepresent Invention. Again we see that the lead iodide is well within theusable range, and that even more surprisingly, its sensitivity is of thesame order of magnitude as a lead iodide PVD detector.

As with mercuric iodide discussed above, it has been found that thedirect precipitation of the starting wide band gap semiconductormaterial, lead iodide, bismuth iodide, or thallium bromide, from aqueoussolution is important in preparing high-quality semiconductor PIBcomposite detectors. The precipitated particles are not ground ensuringthe retention of their crystalline perfection. Direct precipitationensures small grain size, something that prior art preparation methods,such as repeated sublimation and condensation are unable to achieve. Thesize of repeatedly sublimed and condensed mercuric or lead iodidegrains, for example, is usually 50-300 microns; grinding is required toobtain smaller grain sizes. Grinding however, alters the morphology ofthe resulting grains and induces plastic deformations. Thesedeformations may act as electron traps, interfering with the sensitivityof the composite detector plates made with such ground grains.Alternatively, or additionally, a phase transformation can occur underthe shear stress induced by grinding with the resultant phase being lessresponsive to photo-conduction.

Smaller grain sizes may be obtained by precipitating Pbl₂ or othersemiconductors directly from aqueous solution. Starting with solutions,often stoichiometrically matched molar solutions, of lead nitrate andpotassium iodide, e.g. a solution of 0.3 M Pb(NO₃)₂ and a solution of0.6 M KI, small grain size Pbl₂ is obtained. The starting iodide andnitrate should be at least 99% pure or more preferably 99.9% pure, andsuch purities are readily available commercially. The two reagents areadded slowly and the resulting solution is mixed vigorously using, forexample, a mechanical or magnetic stirrer. The solution is then allowedto stand. The precipitated Pbl₂ is washed with water, filtered, anddried. The washing, filtering and drying cycles can be repeated a numberof times but no additional purification procedures are needed. In thecase of Pbl₂, the precipitate so formed has grains having a plateletstructure, which is generally less than 5 microns in its largestdimension. These platelets do not require further fractionation by size.In the case of other semiconductors such as Hgl₂, the dried precipitatedmaterial is sieved and separated into fractions based on grain size. Thepreferred fraction for preparing composite detectors are semiconductorparticulates having grain diameters or other largest dimension of 100microns or less, or more preferably 15 microns or less, 10 microns orless or 5 microns or less.

While the above has discussed precipitation from aqueous solution, thisshould be considered as exemplary only and not limiting. Similarly, thesalts discussed herein as raw materials for the production of smallgrain semiconductor particles are to be considered as exemplary only andnon-limiting. It is readily appreciated that other soluble saltspossessing the required cation or anion can also be used. Precipitationof the semiconductor can be effected from many non-aqueous solvents, ormixed non-aqueous solvent systems or mixed aqueous-non-aqueous solventsystems as well, when suitably soluble starting salts are used.Non-aqueous solvents that can alternatively be used include, forexample, acetone, methanol, ethanol, dimethyl sulfoxide, and toluene.

The powder obtained is subsequently mixed with a binder, generally anorganic binder, but other binders such as silicon based binders can beused as well. Binders which can be used include binders chosen from thefollowing classes: acrylic and methacrylic ester polymers, polymerizedester derivatives of acrylic and alpha-acrylic acids, polymerized butylmethacrylates, chlorinated rubber, vinyl polymers and co-polymers suchas polyvinyl chloride and polyvinyl acetate, cellulose esters andethers, alkyd resins, polymeric urethanes, polymeric styrenes andsilicones. Mixtures of such resins or mixtures of such resins andconventional plasticizers, such as phthalates, adipates and phosphates,may also be used. Particularly preferable as binders are polystyrene andHumiseal® 1B12, the latter being a polyacrylic-polyvinyl blend.

When polystyrene is used as the binder, a mixture of, for example, 25 wt% of the polymer in toluene is prepared. In order to obtain fasterdissolution of the polystyrene in toluene, the mixture can be heatedgently and then slowly cooled to room temperature. The semiconductorpowder prepared as described above is then mixed in the weight ratio ofsemiconductor to dried polystyrene of between 4.4:1 and 26.0:1,preferably between 6.6:1 and 19.8:1 and even more preferably 9.0:1 and15.4:1. Similar ratios can be used with other binders. The material ismixed thoroughly to wet all of the semiconductor powder and to obtain ahomogenous mixture.

The TFT flat panel arrays or CCD substrate may be coated with a thin tielayer of an adhesive such as Humiseal® 1B12, although otherpolyacrylics, polyvinyls, polyurethanes, polyimides, silanes,cyanoacrylics, polyesters, neoprene rubbers or mixtures thereof may beused instead. The adhesive is generally applied by dipping the substrateinto a dilute solution of the adhesive and evaporating off the solvent.Additionally, the adhesive can often be spin coated onto the substrate.Alternatively, the adhesive can be painted or sprayed on above thebottom pixel electrodes. After the adhesive is applied, thesemiconductor PIB composite is placed onto the adhesive layer by any ofthe methods described herein above.

In order to achieve extended lifetimes for the imager, both the bottomand top electrodes are preferably made of indium-tin oxide (ITO), gold,carbon, silicon, germanium, chromium, nickel, platinum or palladium.These materials do not react significantly with wide band gapsemiconductors. It is inadvisable to use titanium-tungsten alloy (Ti—W),In, Al, or Cu because these materials can react with some wide band gapsemiconductor PIB composites.

EXAMPLE 7

7.3 g of Pb(NO₃)₂ (Aldrich Chemicals, 99% pure) was added to a beakercontaining 800 ml of de-ionized water, while 7.3 g of KI (Acros, 99%pure) was dissolved in a second beaker containing 200 ml of de-ionizedwater. Both solutions were heated to 100° C. and subsequently mixedtogether at that temperature. A yellow precipitate, Pbl₂, in the form ofthin, crystalline platelets precipitated out of the solution after thesolution was cooled to room temperature and left standing for 24 hours.The precipitate was filtered and washed with 500 ml. de-ionized water atroom temperature for 10 minutes. After washing, the precipitate wasfiltered again and left to dry in air for 48 hours at room temperature.Nine grams of yellow, plate-like, Pbl₂, micro-crystals were obtained.

A yellow paste was obtained by taking 5 grams of the above Pbl₂precipitate and mixing it with about 2.5 ml of 25 wt %polystyrene/toluene solution. A 400 micron thick layer of this paste wasscreen printed onto an indium-tin oxide (ITO) electrode, the lattercovering a glass substrate. Screen printing was effected as describedherein above. The Pbl₂ layer was dried for 100 hours in air at roomtemperature.

Electrodag®, a graphite methyl ethyl ketone based dispersion, waspainted onto the lead iodide PIB layer and the solvent allowed toevaporate leaving a continuous carbon electrode. A platinum wire wasthen attached to the Electrodag® electrode using any one of severalcommercially available conducting glues. After drying the Electrodag®electrode at room temperature in air for 48 hours, the detector wasready for making measurements.

EXAMPLE 8

As in Example 7, but instead of screen printing the Pbl₂/polystyrenepaste, the paste was applied with a doctor blade assembly similar to theone shown in FIG. 4.

EXAMPLE 9

As in Example 7, but instead of screen printing the Pbl₂/polystyrenepaste, the paste was applied in a die press similar to the one shown inFIG. 3.

EXAMPLE 10

As in Example 7, but instead of applying the Pbl₂/polystyrene paste ontoa glass substrate covered with an ITO electrode, the paste was appliedonto a CCD pixel array.

EXAMPLE 11

As in Example 7, but instead of using polystyrene as the binder in thePIB composite material, Humiseal®, a commercially availablepolyacrylic-polyvinyl polymeric mixture diluted with toluene and methylethyl ketone, was used as the binder. The Humiseal/Pbl₂ ratio was thesame as in Example 7 and the detector was pressed in a die press.

EXAMPLE 12

As in Example 7, but instead of using a continuous carbon upperelectrode, a gold electrode was sputtered onto the Pbl₂ PIB compositeusing a magnetron sputtering machine.

EXAMPLE 13

150 ml of 70% nitric acid was added to 400 ml of de-ionized water In abeaker, and mixed. 70 grams of BiO(NO₃) (Merck) was added to the dilutednitric acid solution. Twenty grams of KI (Acros 99% pure) was dissolvedat room temperature in another beaker, this one containing 100 ml ofde-ionized water. The KI solution was then added to 100 ml of thebismuth solution and the resulting mixture was stirred for two minutesat room temperature and allowed to stand. A black precipitate wasobtained.

The precipitate was filtered and washed in 400 ml of 7% nitric acid forthree hours. After washing, the precipitate was filtered again and driedfor 72 hours at room temperature. Twenty grams of the dry, black,slightly agglomerated Bil₃ powder was obtained. The powder agglomerateswere easily broken apart with a plastic spoon.

4.5 grams of the black Bil₃ powder was mixed with about 2 ml of 25 wt %polystyrene/toluene solution and a black paste was obtained. The blackpaste was screen printed as described hereinabove onto an ITO electrodecoated on a glass substrate. The layer was dried in air at roomtemperature for 100 hours.

Electrodag®, a graphite methyl ethyl ketone based dispersion, was coatedonto the top of the Bil₃-polystyrene PIB layer to form an electrodelayer. After the electrode layer was dried, a platinum wire wasconnected to the carbon electrode using any one of several commerciallyavailable conductive glues. After drying in air at room temperature for48 hours, the composite detector was ready for use.

EXAMPLE 14

Equal volumes of a 0.6 M aqueous solution of HgCl₂ and a 1.2 M aqueoussolution of KI were mixed quickly in a container and allowed to stand.The Hgl₂, which precipitated out of the solution, was washed with water,filtered and dried, the washing, filtering and drying cycle beingrepeated three times. The mixture was then sieved, shaken and separatedinto fractions by grain size. The fraction passing through a 20 micronsieve was used and microscopic inspection of that fraction showed thatmore than 90% of the particles had a diameter of 5 microns or less.About 10 grams of mercuric iodide particles were then mixed with about 5ml of 25 wt % polystyrene/toluene solution. The homogeneous mixtureobtained had a weight ratio of Hgl₂ to dry polystyrene of about 9:1.

A TFT pixilated substrate was coated with indium-tin oxide (ITO), and athin adhesive tie layer (Humiseal® 1B12) was applied thereto. The ITOlayer served as the bottom pixel electrode. The pixels had a size ofabout 100×100 microns, each pixel separated from its neighbors by about10 microns. The adhesive tie layer had a thickness of less than 0.5micron and was applied by dipping the bottom pixel electrodes of thesubstrate into a dilute solution of the adhesive from which the solventwas subsequently allowed to evaporate.

The adhesive coated TFT substrate was then placed in a die press similarto the one shown in FIG. 3, and the mercuric iodide—polystyrenecomposite mixture was deposited on top of the Humiseal® tie layer. Thedetector plate had a final thickness of 150 microns and an active areaof 2″×2″. Placing a spacer having the desired thickness in the diecontrolled the thickness of the plate.

The detector plate was then removed from the die and allowed to dry atroom temperature. After drying, a continuous upper electrode of gold wasapplied by vacuum evaporation. A thin Pt wire was attached to the uppercontinuous electrode using a conductive glue, the Pt wire serving as ahigh voltage bias contact.

Surprisingly, it has been found that the sensitivity of PIB compositedetectors discussed herein above can be maintained over longer timeperiods when a separate base layer is used. The base layer is placedadjacent to the bottom electrode and/or substrate and underneath aprimary composite layer. Typically, the primary layer is a mercuriciodide PIB composite layer but other semiconductor PIB composite layerscan also be used. The base layer, hereinafter called a “buffer” layer,typically is a lead iodide PIB composite layer. Alternatively, other“buffer” layers such as bismuth iodide or thallium bromide PIB compositelayers can be used. The preparation of these layers and theirapplication to the electrode or substrate have been described hereinabove. Where necessary, an adhesive layer comprised of any of theadhesives discussed above can be used to adhere the buffer layer to theelectrode or substrate. Additionally, where necessary to preventdelamination, an adhesive layer can be positioned between the buffer andprimary layers. These mixed semiconductor PIB composite multilayerdetectors may hereafter be called “hybrid detectors”.

Reference is now made to FIG. 14 where a photoconducting hybrid bi-layerdetector plate 10 for an X-ray imaging system produced according to thepresent invention is shown. Detector plate 10 consists of a TFTsubstrate 1 having metallic pixels (not shown), the latter functioningas the bottom electrode of detector 10. The bottom pixel electrode iscoated with a tie layer 3, such as Humiseal® 1B12 (a polyacrylic,polyvinyl mixture in a mixed methyl ethyl ketone/toluene solvent). Tielayer 3 acts as an adhesive to prevent a Pbl₂ PIB layer 4 from peelingoff the electrode. Tie layer 3 is usually less than 0.5 micron and isgenerally applied by dipping the substrate into a dilute solution of theadhesive, from which the solvent is then allowed to evaporate.Alternatively, tie layer 3 can be painted onto the upper surface of thebottom pixel electrode.

A PIB layer consisting of a Hgl₂ PIB composite 5 is applied directlyonto the PIB buffer layer 4 consisting of Pbl₂ PIB composite 5. Both PIBlayers 4 and 5 can be applied by any of the methods described herein.These methods include, but are not limited to, use of a doctor blade,die press, Mayer blade, slot coater or screen printer (SP). A vacuumdeposited, painted or sprayed continuous upper electrode 6 coversmercuric iodide PIB composite layer 5 on the side distal from substrate1. A high voltage platinum bias wire 7 is attached to upper electrode 6using any suitable conductive glue 8. A number of such glues arecommercially available. Optionally, the complete detector plate 10 canbe encapsulated, as described above, with insulating, Inert material(not shown) and connected to a pixel array readout unit. The device inFIG. 14 can form part of the typical pixel equivalent circuit 40 shownin FIG. 2 discussed above.

Reference is now made to FIG. 15 where the sensitivity versus biaspolarity of a Hgl₂/Pbl₂/substrate hybrid is shown. The relative smalldifferences in sensitivities when the two polarities are used is readilyapparent. The bi-polarity enables easier application of these compositesto TFT's designed for positive polarity. Theoretically, exploiting thisbi-polarity allows for greater charge collection efficiency.

In the above description of multiple layers, the discussion has focusedon bi-layer structures. It should readily be apparent to one skilled inthe art that, when necessary, there can be more than two semiconductorPIB layers in a detector. For example, there may be occasions when alead iodide PIB layer (or a bismuth iodide PIB layer or a thalliumbromide PIB layer or a CZT PIB layer) is placed above a mercuric iodidePIB layer, proximate to the upper conducting electrode, forming atri-layer.

In yet other embodiments the layers need not be discrete layers. Asubstantially uniform mixture of two or more different semiconductor PIBcomposites can be made and applied directly over an electrode and/orsubstrate. The resulting mixture of semiconductor PIBs can have thedesirable feature of increasing the effective working-life of a detectorwithout significantly reducing sensitivity.

EXAMPLE 15

Ten grams of Pbl₂ powder, prepared as in Example 7 above, was mixed withabout 3 ml of 25 wt % polystyrene/toluene solution resulting in a yellowpaste. A 200 micron thick layer of this lead iodide PIB paste was diepressed onto the surface of a 1″×3″ indium-tin oxide (ITO) coated glasssubstrate that had been placed in a die mold as illustrated in FIG. 3and discussed hereabove.

Equal volumes of a 0.6 M aqueous solution of HgCl₂ and a 1.2 M aqueoussolution of KI were mixed quickly in a beaker and left to stand. TheHgl₂ which precipitated out was washed with water, filtered and dried.Ten grams of the dried Hgl₂ were mixed with about 3 ml of a 25 wt %polystyrene/toluene solution. The weight ratio of dry polystyrene tosemiconductor in the composite was 15.4:1, corresponding to a volumeratio of polystyrene/Hgl₂ of 30:70. A homogenous paste was obtained.

The mercuric iodide/polystyrene PIB colloidal dispersion was cast on topof the Pbl₂ PIB ITO coated substrate previously prepared and placed in adie press. The Pbl₂ PIB composite coating the substrate was prepared asdescribed in Example 9. The mercuric iodide PIB composite layer waspressed onto the lead iodide layer and a bi-layer “hybrid” detectorplate was produced.

At the outset, prior to depositing the lead iodide layer, the substratewas coated with ITO to which a thin adhesive tie layer (Humiseal® 1B12)was applied. The ITO layer acted as the bottom pixel electrode. Eachpixel had a size of about 100×100 microns and was separated by about 10microns from its nearest neighbors in each direction. The adhesive tielayer had a thickness of less than 0.5 micron and was applied by dippingthe bottom pixel electrodes of the substrate into a dilute solution ofthe adhesive, after which the solvent was allowed to evaporate. Theadhesive tie layer acted as a glue preventing peeling of the lead iodidePIB buffer layer from the bottom pixel electrodes.

The detector plate was then removed from the die press and allowed todry at room temperature. After drying, a continuous upper electrode ofgold was applied by vacuum evaporation. A thin Pt wire was attached tothe upper continuous electrode using a conductive glue; the Pt wireserved as a high voltage bias contact.

The final, overall thickness of the detector plate thus formed was 400microns. Placing spacers in the die controlled the thickness of the PIBlayer.

EXAMPLE 16

As in Example 15, except that the PIB buffer layer was a composite Bil₃layer prepared according to the method described in Example 13.

EXAMPLE 17

As in Example 15, but instead of applying the Pbl₂ PIB buffer layer andthe Hgl₂ PIB layer using a die press, the PIB layers were applied with adoctor blade assembly similar to the one shown in FIG. 3.

EXAMPLE 18

As in Example 15, but instead of applying the Pbl₂ PIB buffer layer andthe Hgl₂ PIB layer using a die press, the PIB layers were applied by ascreen printing apparatus similar to the one shown in FIG. 5.

EXAMPLE 19

As in Example 15, but instead of depositing the Pbl₂ PIB buffer layerand the Hgl₂ PIB layer onto a TFT substrate array, the mixture was caston a CCD pixel array with pixel dimensions similar to that disclosed inExample 15.

EXAMPLE 20

As in Example 15, but instead of using polystyrene as the binder in thePIB composite, Humiseal®, a polyacrylic-polyvinyl polymeric mixture,diluted with a toluene/methyl ethyl ketone mixed solvent, was used. TheHumiseal®/semiconductor ratio was the same as in Example 15 and thedetector was pressed in a die press.

EXAMPLE 21

As in Example 15, but instead of using vacuum evaporated gold as thecontinuous upper electrode, magnetron sputtered gold was used as thecontinuous upper electrode.

EXAMPLE 22

Bil₃ powder and a bismuth iodide BIP composite made from that powderwere prepared as in Example 13. The resulting black paste was spreadonto an ITO coated glass substrate that was been pre-coated with anadhesive tie layer material. The PIB covered substrate was compressed toa desired thickness by pressing the PIB covered substrate in a die-pressthereby forming a buffer layer. After drying in air for 4 days, a Hgl₂PIB composite layer similar to that obtained in Example 1 was placed asa primary layer over the Bil₃—PIB composite and spread to the desiredthickness using a doctor blade assembly. A gold electrode was appliedusing sputtering.

While the present invention has been described herein above in terms ofwide band gap semiconductors synthesized by precipitation from solution,the method of preparation discussed and the examples described should beviewed as illustrative only and non-limiting. It is readily appreciatedby one skilled in the art that any method of preparing these wide bandgap semiconductors which results in small grains of the size definedherein, can also be used.

Imaging systems made with detector plates using the composites or hybridcomposites of the present invention can have a multiplicity of uses.Among these applications are mapping X-ray emission and gamma burstsfrom solar and extra-galactic sources, identification of counterfeitbanknotes, identifying paintings and archeological artifacts anddetecting nuclear materials. These systems can be used in nuclearmedicine and in operating procedures such as tumor removal, transplantperfusion, vascular graft viability, among others. Because the plates donot contain single crystal materials, they can be used to fabricate thelarge detectors required in many applications at substantially reducedcost.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather the scope of the present invention isdefined only by the claims that follow:

1. An imaging composition for radiation detection systems whichcomprises an admixture of at least one non-heat treated, non-groundparticulate semiconductor with a polymeric binder, said at least onenon-heat treated, non-ground particulate semiconductor selected from agroup consisting of mercuric iodide, lead iodide, bismuth iodide,thallium bromide and cadmium-zinc-telluride (CZT), and wherein at least90% of said semiconductor particulates have a grain size of less than100 microns in their largest dimension.
 2. An imaging compositionaccording to claim 1, which possesses at least one of the followingfeatures: (i) said polymeric binder is an organic polymeric binder; (ii)at least 90% of said semiconductor particulates have a grain size ofless than 15 microns in their largest dimension; (iii) said compositionfurther comprises at least one organic solvent; (iv) the weight ratio ofsaid semiconductor particulates to said binder is from about 4.4:1 toabout 26.0:1.
 3. An imaging composition according to claim 2, whichpossesses at least one of the following features: (i) said organicpolymeric binder comprises at least one polymer selected from a groupconsisting of polystyrene, polyurethane, alkyd polymers, cellulosepolymers, and acrylic and vinyl polymers and co-polymers and mixturesthereof; (ii) at least 90% of said semiconductor particulates have agrain size of less than 10 microns in their largest dimension; (iii)said at least one organic solvent is selected from aliphatic alcohols,ethers, esters, ketones and aromatic and heterocyclic solvents; (iv) theweight ratio of said semiconductor particulates to said binder is fromabout 6.6:1 to about 19.8:1.
 4. An imaging composition according toclaim 2, which possesses at least one of the following features: (i)said organic polymeric binder comprises at least one polymer selectedfrom a group consisting of polystyrene, polyurethane, and acrylic andvinyl homo- and co-polymers and mixtures thereof; (ii) at least 90% ofsaid semiconductor particulates have a grain size of less than 5 micronsin their largest dimension; (iii) said at least one organic solvent isselected from aliphatic alcohols, ethers, esters, ketones and aromaticand heterocyclic solvents; (iv) the weight ratio of said semiconductorparticulates to said binder is from about 9:1 to about 15.4:1.
 5. Animaging composition according to claim 1, wherein said semiconductorparticulates are precipitated from a solution.
 6. An imaging compositionaccording to claim 5, wherein said solution has a solvent which ischosen from a group consisting of water, a non-aqueous solvent, a mixedaqueous-non-aqueous solvent and a mixed non-aqueous solvent.
 7. Aradiation detector plate for an imaging system including: at least onesubstrate, said substrate serving as an electrode; at least one imagingcomposition layer of an imaging composition applied onto said substrate,said composition including: at least one particulate semiconductor, saidsemiconductor comprising non-ground, non-heat treated particulates atleast 90% of which are below 100 microns in their largest dimension andwherein said semiconductor is chosen from a group consisting of bismuthiodide, lead iodide, mercuric iodide, thallium bromide andcadmium-zinc-telluride (CZT); and a polymeric binder, said semiconductorparticulates being in an admixture with said binder; and a secondelectrode, said second electrode in electrical connection with saidcomposition and connected to a high voltage bias.
 8. A radiationdetector plate according to claim 7, which additionally comprises atleast one composition layer comprising non-heat treated, non-groundparticulate mercuric iodide in admixture with a polymeric binder.
 9. Aradiation detector plate according to claim 7, wherein said at least onecomposition layer comprises at least two semiconductors selected from agroup consisting of bismuth iodide, lead iodide, mercuric iodide,thallium bromide and cadmium-zinc-telluride (CZT).
 10. A radiationdetector plate according to claim 7, wherein said at least onecomposition layer comprises at least two discrete composition layers,each of said discrete layers comprised of at least one semiconductorselected from a group consisting of bismuth iodide, lead iodide,mercuric iodide, thallium bromide and cadmium-zinc-telluride (CZT). 11.A radiation detector plate according to claim 10, further including anadhesive layer between said at least two discrete composition layers.12. A radiation detector plate according to claim 10, wherein said atleast two discrete composition layers comprise at least one discretecomposition layer in which said semiconductor is non-heat treated,non-ground particulate lead iodide and at least one discrete compositionlayer in which said semiconductor is non-heat treated, non-groundparticulate mercuric iodide.
 13. A radiation detector plate according toclaim 7, which further comprises an adhesive tie layer applied to saidsubstrate.
 14. A radiation detector plate according to claim 13, whereinsaid tie layer is chosen from a group consisting of polyacrylics,polyvinyls, polyurethanes, polyimides, cyanoacrylics, silanes,polyesters, and neoprene rubbers and mixtures thereof to bind saidcomposition layer to said substrate.
 15. A radiation detector plateaccording to claim 13, wherein said tie layer is a polyacrylic-polyvinylmixture.
 16. A radiation detector plate according to claim 13, whereinsaid tie layer is a silane.
 17. A radiation detector plate according toclaim 13, wherein said composition layer is applied onto said adhesivelayer on the side of said adhesive layer distal from said substrate. 18.A radiation detector plate according to claim 7, wherein said at leastone substrate is coated with a uniform, thin film of electricallyconducting material selected from a group consisting of palladium, gold,platinum, indium-tin oxide (ITO) and germanium.
 19. A radiation detectorplate according to claim 7, wherein said second electrode comprises auniform, thin film of electrically conducting material selected from agroup consisting of carbon, palladium, gold, platinum, indium-tin oxide(ITO) and germanium.
 20. A radiation detector plate according to claim7, wherein said second electrode is applied by a method selected from agroup consisting of sputtering, evaporation, spraying and painting. 21.A radiation detector plate according to claim 7, wherein said at leastone substrate is chosen from a group consisting of a thin filmtransistor (TFT) flat panel array, a charge coupled device (CCD),complementary metal oxide semiconductor (CMOS) array and an applicationspecific integrated circuit (ASIC).
 22. A radiation detector plateaccording to claim 7, wherein said at least one composition layerpossesses at least one of the following features: (i) said polymericbinder is an organic binder; (ii) at least 90% of said semiconductorparticulates have a grain size of less than 15 microns in their largestdimension.
 23. A radiation detector plate according to claim 22, whereinsaid at least one composition layer possesses at least one of thefollowing features: (i) said organic polymeric binder comprises at leastone polymer selected from a group consisting of polystyrene,polyurethane, alkyd polymers, cellulose polymers, and acrylic and vinylhomo- and co-polymers and mixtures thereof; (ii) at least 90% of saidsemiconductor particulates have a grain size of less than 10 microns intheir largest dimension.
 24. A radiation detector plate according toclaim 22, wherein said at least one composition layer possesses at leastone of the following features: (i) said organic polymeric bindercomprises at least one polymer selected from a group consisting ofpolystyrene, polyurethane, and acrylic and vinyl homo- and co-polymersand mixtures thereof; (ii) at least 90% of said semiconductorparticulates have a grain size of less than 5 microns in their largestdimension.
 25. A radiation detector plate according to claim 7, whereinsaid at least one composition layer is prepared at room temperature. 26.A radiation detector plate according to claim 7, wherein said at leastone composition layer is prepared at temperatures below 60° C.
 27. Aradiation detector plate according to claim 7, wherein said at least onecomposition layer has a thickness of 40-3000 microns.
 28. A radiationdetector plate according to claim 7, wherein said system can detectradiation in the 6 keV to 15 MeV range.
 29. An image receptor for animaging system, comprising at least one composition layer, said layercomprising an imaging composition as defined in claim 1, saidcomposition layer positioned on a conductive substrate layer, saidsubstrate layer forming a bottom electrode, and said composition layercovered by an upper conductive layer forming an upper electrode, whereinat least one of said conductive layers is provided with a plurality ofconductive areas separated from each other by a plurality ofnon-conductive areas, and wherein a multiplicity of said conductiveareas are individually, connected, via a charge-sensitive pre-amplifier,to an imaging electronic system.
 30. An image receptor according toclaim 29, which is further characterized by at least one of thefollowing features: (i) said conductive areas are separated from eachother by a dielectric material; (ii) said conductive substrate layer iscovered with a uniform, thin film electrode layer selected from a groupconsisting of palladium, gold, platinum, indium-tin oxide (ITO) andgermanium; (iii) said image receptor is adapted for use in an imagingsystem selected from X-ray and gamma ray imaging systems; (iv) in saidat least one composition layer, said polymeric binder is an organicbinder; (v) in said at least one composition layer, at least 90% of saidsemiconductor particulates have a grain size of less than 15 microns intheir largest dimension; (vi) an adhesive tie layer between saidcomposition layer and said bottom electrode, said tie layer chosen froma group consisting of polyacrylics, polyvinyls, polyurethanes,polyimides, cyanoacrylics, silanes, polyesters, and neoprene rubbers andmixtures thereof to bind said composition layer to said electrode. 31.An image receptor according to claim 30, wherein said at least onecomposition layer possesses at least one of the following features: (i)said organic polymeric binder comprises at least one polymer selectedfrom a group consisting of polystyrene, polyurethane, alkyd polymers,cellulose polymers, and acrylic and vinyl homo- and co-polymers; (ii) atleast 90% of said semiconductor particulates have a grain size of lessthan 10 microns in their largest dimension; (iii) comprises at least onepolymer selected from a group consisting of polyurethane, polystyrene,and acrylic and vinyl homo- and co-polymers.
 32. An image receptoraccording to claim 30, wherein said at least one composition layerpossesses at least one of the following features: (i) said organicpolymeric binder comprises at least one polymer selected from a groupconsisting of polystyrene, polyurethane, alkyd polymers, cellulosepolymers, and acrylic and vinyl homo- and co-polymers; (ii) at least 90%of said semiconductor particulates have a grain size of less than 5microns in their largest dimension; (iii) comprises at least one polymerselected from a group consisting of polyurethane, polystyrene, andacrylic and vinyl homo- and co-polymers.
 33. An image receptor accordingto claim 29, which additionally comprises at least one composition layercomprising non-heat treated, non-ground particulate mercuric iodide inadmixture with an organic polymeric binder.
 34. An image receptoraccording to claim 29, wherein said at least one composition layercomprises at least two said semiconductors selected from bismuth iodide,lead iodide, mercuric iodide, thallium bromide andcadmium-zinc-telluride (CZT).
 35. An image receptor according to claim29, wherein said at least one composition layer comprises at least twodiscrete composition layers, each of said discrete layers comprised ofat least one semiconductor selected from a group consisting of bismuthiodide, lead iodide, mercuric iodide, thallium bromide andcadmium-zinc-telluride (CZT).
 36. An image receptor according to claim35, further comprising an adhesive layer between said two discretecomposition layers.
 37. An image receptor according to claim 35, whereinsaid at least two discrete composition layers comprise at least onediscrete composition layer where said semiconductor is non-heat treated,non-ground particulate lead iodide and at least one discrete compositionlayer where said semiconductor is non-heat treated, non-groundparticulate mercuric iodide.
 38. An image receptor according to claim29, wherein said substrate is chosen from a group consisting of a thinfilm transistor (TFT) flat panel array, a charge coupled device (CCD),complementary metal oxide semiconductor (CMOS) array and an applicationspecific integrated circuit (ASIC).
 39. An image receptor according toclaim 29, wherein said receptor is prepared at room temperature.
 40. Animage receptor according to claim 29, wherein said receptor is preparedat temperatures below 60° C.
 41. An image receptor according to claim29, wherein said receptor can image radiation from about 6 keV to about15 MeV.
 42. A method for preparing a radiation detector plate, saidmethod including the steps of: providing a substrate; placing asemiconductor imaging composition onto said substrate thereby forming acomposition layer, wherein the imaging composition comprises anadmixture of at least one non-heat treated, non-ground particulatesemiconductor with a polymeric binder, said at least one non-heattreated, non-ground particulate semiconductor selected from a groupconsisting of mercuric iodide, lead iodide, bismuth iodide, thalliumbromide and cadmium-zinc-telluride (CZT), and wherein at least 90% ofsaid semiconductor particulates have a grain size of less than 100microns in their largest dimension: applying an electrode to saidcomposition layer on the side distal from said substrate; and connectinga high voltage bias connection to said electrode.
 43. A method forpreparing a radiation detector plate according to claim 42, furthercomprising the step of applying an adhesive tie layer to said substrateprior to said placing step.
 44. A method for preparing a radiationdetector plate according to claim 42, wherein said placing step furthercomprises a step of die pressing said composition to form saidcomposition layer.
 45. A method for preparing a radiation detector plateaccording to claim 42, wherein said placing step further comprises astep of slot die coating said composition to form said compositionlayer.
 46. A method for preparing a radiation detector plate accordingto claim 42, wherein said placing step further comprises a step ofspreading said composition with a doctor blade to form said compositionlayer.
 47. A method for preparing a radiation detector plate accordingto claim 42, wherein said placing step further comprises a step ofspreading said composition with a Mayer rod to form said compositionlayer.
 48. A method for preparing a radiation detector plate accordingto claim 42, wherein said placing step further includes the step ofscreen printing said composition to form said composition layer.
 49. Amethod for preparing a radiation detector plate according to claim 42,wherein said placing step includes a series of placing steps each ofsaid steps forming another composition layer.
 50. A method for preparinga radiation detector plate according to claim 42, further comprising thestep of depositing an electrically conductive material on said substratebefore said placing step.